数学题1+3+5+.+(2n-1)=?
3个回答
用这个公式,aN=a1N+N(N-1)d/2
aN=a1+(N-1)d
N=(aN-a1)/d+1
对此题N=n
aN=1*n+n(n-1)*2/2=n+n(n-1)=n^2
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